Electric match assembly and electric explosion initiators made therewith



Jan. 3, 1967 Y w. D. TREVORROW 3,295,447 ELECTRIC MATCH ASSEMBLY ANDELECTRIC EXPLOSION INITIATORS MADE THEREWITH Filed April 6. 1965 2Sheets-Sheet 1 INVENTOR. Will ium D. Trevorrow @wAXQ. SSMUSJY Ji-In-1967 W D. TREVORROW 3,295,447

ELECTRIC MATCH :ASSEMBLY AND ELECTRIC EXPLOSION INITIATORS MADETHEHEWITH' Filed April 6, 1965 2 Sheets-Sheet 2 FIG. 3 FIG'.4

} INVENTOR. Willlcm D. Trevorrow :ELECTRIC MATCH United States Patent3,295,447 ASSEMBLY AND ELECTRIC EXPLOSION INITIATORS MADE THEREWITHWilliam D. Trevorrow, Tamaqua, Pa., assignor to Atlas ChemicalIndustries, Inc., Wilmington, Del., a corporation of Delaware Filed Apr.6, 1965, Ser. No. 446,797 21 Claims. (Cl. 102-28) This application is acontinuation-in-part of application -Ser. No. 368,751, filed May 4, 1964which in turn is a continuation-impart of application Ser. No. 313,493,filed Oct. 3, 1963, now abandoned.

The present invention relates to an improved electric match assemblywhich contains an electrical bypass. A portion of the bypass path isthrough a semi-conductive material. The present invention also relatesto an electric explosion initiator which incorporates the presentimproved match assembly.

The danger of extraneous electrical energy in blasting circuits has longbeen recognized. The ignition compositions generally used incommercially available initiators arehighly heat sensitive and exposureof the bridge wire to extraneous electricity is quite capable ofigniting the ignition composition and subsequently firing the initiator.

Although the danger from accidental firing of detonators by extraneouselectricity is present in almost all blasting operations, the danger isparticularly present when the blasting operation is carried out underconditions conducive to high levels of either atmospheric staticelectricity, for example, in electrical, dust or snow storms; or, inoperations susceptible to the generation of static charges, for example,operations wherein a particulate blasting agent, such as sensitizedammonium nitrate is blowloaded, e.g., loaded into a bore hole by astream of compressed air.

A number of solutions to the problem of static susceptibility ofelectric detonators are known, and most solutions have been effective atleast to some degree. However, none have been found to be entirelysatisfactory when cost, ease of manufacture, effectiveness, and storagelife areall considered.

One means of protecting an electric initiator from premature initiationby extraneous static charges has been by means of a semi-conductive plugpositioned within the detonator shell surrounding and in intimatecontact with bared portions of the leg Wires and extending to closeproximity with the inside shell wall. The plug is spaced from the shellwall by a distance substantially less than the distance between eitherof the leg wires and the shell Wall in the locus of the ignitioncomposition. Thus, a static charge may be conducted to the edge of thesemiconductive plug-body and allowed to discharge to the shell wall. Inthis manner the static charge may be grounded to the shell outside thelocus of the ignition composition.

The term semi-conductive as used herein describes the property of amaterial to act as an insulator at low voltages, for example, up to 100volts, but act as a low resistance material when exposed to highvoltages comparable to those required to initiate an initiator by acharge of static electricity. A semi-conductive material presents aconductive path for high voltage, static discharges and a highresistance path to a low voltage of the type used normally to fire theinitiator.

A typical protective plug of the prior art is a semiconductive body madeup of a wax matrix and including a quantity of finely divided conductivematerial therein. Examples of the finely divided conductive materialsgenerally used are powdered aluminum, carbon, galena, brass or copper. Aserious disadvantage of the prior art protective plugs is the difficultyof maintaining intimate con- 3,295,447 Patented Jan. 3, 1967 tactbetween the leg wires and the protective plug, particularly during theinitiator manufacturing process wherein the various component parts areassembled. Generally the greater the quantity of conductive material ina plug, the greater the degree of static protection which is obtained.However, the plugs become more brittle with an increase in content ofconductive material. Brittleness causes ruptures or cracks extendingalong the interface between the leg Wires and the protective plug whichreduce the area of intimate contact between the leg wires and the plug.This condition markedly and adversely affects the efliciency of the plugto afford protection against static charges. Prior art plugs are oftenbrittle and susceptible to cracking or splitting when the leg wirestherein are subjected to a very slight pull or tug of A to pound. It ismost difiicult to assemble an initiator containing a prior artprotective plug and not expose the leg wires positioned through the plugto slight tugs suflicient to crack the plug. The present inventionprovides a means of efliciently positioning a plug of semi-conductivematerial between the electrical lines to rotect the initiator fromextraneous static charges. The present means may be entirelyincorporated in a match head of standard dimensions. The presentinvention also provides intimate support of the semi-conductive plug inall directions which drastically lessens any chance of a crack or splitin the plug during assembly and later handling. The present inventionalso allows the incorporation of a large, up to 99% by weight, amount ofconductive material in the semi-conductive plug.

It has also been discovered that various malfunctions of delay electricinitiators, which are seemingly unrelated, are caused by a large amountof heat, generated by an electrical are which occurs within theinitiator when an excessive electrical current is supplied. The gasesfrom the ignition composition within the initiator are heated rapidlyand a high internal pressure is soon built up. The heat and highpressure condition within the initiator causes either an outward ruptureof the initiator Wall or a violent dislodging of the initiator seal, andthe enclosed hot gases are rapidly released. The eifect of this actionon the blasting operation is unpredictable and varied. The suddenrelease of the gases may create conditions under which the burning delayelement may be' extinguished or the speed of burning of the delayelement is retarded. The delay element will then fail to initiate theexplosive charge of the initiator at the precise time interval. Therelease of the hot gases and flame can ignite the surrounding explosivewhich may slowly burn with the possibility of detonation developing. Ifthe delay element is extinguished and the surrounding explosive chargeis ignited, several minutes may elapse before heat from the burningexplosive either causes detonation or ignites the explosive charge ofthe initiator which initiates the remainder of the burning explosive.Heat generated by the burning explosive may decompose the explosivecharge of the initiator, and, in such case, the surrounding explosivemay, unpredictably, either burn completely or detonate at any pointbefore it is completely consumed by burning. If the burning element isextinguished by the sudden release of the entrapped gases, and theexplosive charge is not ignited by the hot gases, the shot may failcompletely. Thus, the occurrence of a violent electrical are within thedelay electric initiator may result in various malfunctions such as: apremature detonation, a misfire, or a delayed voltage across the bridgewire terminals frequently is high enough to sustain an electrical arcafter the bridge wire melts, and, when a power line of high currentcapacity is used, the arc may generate enough heat within the initiatorprior to initiation to cause malfunction. Parallel circuit arrangementsof delay initiators are often used in the blasting art and theconvenience and advantages of a power line as a source of electricalenergy are well-known. Thus, the majority of arcing difiicultiesencountered in blasting operations occur when a commonly used circuitarrangement is combined with a commonly used source of electricalenergy.

In accord with the present invention a match assembly is provided whichincludes an electrical bypass. A portion of the bypass path is through asemi-conductive material. The present match assemblies comprise a pairof conductive tabs which have a bottom portion and a portion broaderthan said bottom portion. The tabs are seperated by a layer ofnonconductive material and have a connecting bridge wire along theirbottom portions. An ignition composition is positioned in ignitablerelation to the bridge wire; The tabs of the present match are in closeelectrical contact with a plug of semioonductive material which connectsone tab with the other. A match assembly of the present invention mayalso include a pair of leg wires individually attached to the tabs andadapted to be connected to a source of electrical energy suitable forfiring the initiator.

The tabs of the present match assembly are preferably fabricated from athin sheet of a metal which can be easily soldered as both the bridgewire and the leg wires need to be attached to the tab. Copper or brassare aptly suited to this use. Preferably, at some point above the bottomportion of the tab, the tab members have a portion broader than thebottom portion. Suitably the tab members may be fabricated in atrapezoidal shape. The layer of non-conductive material which separatesthe tab members may, for example, be paper, fiber, asbestos, or ceramic.The metal tabs and non-conductive layer are suitably in the form of alaminate being adhesively joined. The bridge wire which connects thetabs is preferably a thin wire of high electrical resistance.

The plug of semi-conductive material is preferably comprised of amixture of a finely divided metal and a nonc-onductive matrix material.Although finely-divided metals, such as copper, lead, and iron may beutilized, finely-divided aluminum has been found to be particularlyeffective as the metal component. Finely divided metal oxides may besubstituted for a portion of said metal component to achieve the desiredresults. In the term metal oxides as used herein is included mixed metaloxides such as chromates, manganates and stannates. Various metal oxidesmay be used for this purpose, for example, Pb O Sn O Fe O MnO CuO, K CrO and BaCrO While insulating materials suc has polyethylene may be used,wax has been found to be particularly satisfactory as the non-conductivematrix material. Suitably the wax has a relatively high melting point,for example, natural Waxes such as beeswax and carnauba, and syntheticwaxes such as Acrawax are useful in the present invention. Preferablythe finely divided metal and metal oxides are of a size that will pass anumber 100 U.S.S. screen. Preferably the semi-conductive materialcontains between about 80% and about 99% by weight of the finely-dividedmetal component and between about 1% and about 20% wax. Up to about 50%of the metal component may be substituted with one or more suitablemetal oxides without reducing the susceptibility of the subjectinitiators to static electricity or malfunctions due to arcing. In mostpractical instances where a metal oxide is to be incorporated from about0.5% to about 50% of the metal component is replaced with one or moremetal oxides. The semiconductive material may be produced by initiallythoroughly mixing a finely divided form of the components in theirdesired proportions, pelleting the mixture and then granulating thepellets preferably through a 20 mesh U.S.S. screen. The granulatedmixture is suited to pressure forming operations and may be easilyformed into any desired shape.

In order to maintain close electrical contact and to insure closecontact in a mass produced item the matchbody comprising the tabs andthe non-conductive material separating the tabs is preferably perforatedand the semiconductive material forcefully positioned in theperforation. The semi-conductive material may be forcefully positionedin a perforated mat-ch assembly by placing a perforated match assemblyin a suitable fixture that has a top plate and a hole therethrough,aligning the plate hole and match perforation, and pressing a loosecharge or a preformed pellet of semi-conductive material in the alignedhole and perforation. A pressure in the range of from about 10,000 toabout 30,000 p.s.i. has been found to be aptly suited to use in thepressing operation. The size of the perforation in the match assemblymay vary due to such variables as the size of the assembly, or thecomposition of the semi-conductive material. suitably the plug is of asize that will provide a good path for static electricity across thematch tabs. Generally, positioned plugs having a cross-sectional area ofbetween about 0.0028 and about 0.0078 square inch and generalcylindrical in shape give satisfactory results. Suitably the plug iscylindrical. It may also be preferred, in order to insure closeelectrical contact, that the plug extend slightly on either side of thematch tabs. Generally between about 0.001 and about 0.005" issufficient. In order to insure a good electrical connection between thetabs, the plug and the leg wires, the leg wires may suitably be soldereddirectly on the tab and in contact with the end of the plug.

The present invention also contemplates an electric explosion initiatorwhich includes a match assembly in accord with the present invention.Electric initiators generally comprise a metallic shell member, encasingan explosive charge and a match assembly positioned in firing positionwith the charge. Preferably the explosive charge is comprised of adetonating base charge and a primer charge positioned in initiatingrelation to the base charge. A match assembly in accord with theforegoing description is positioned in igniting relation to the primercharge. Suitably the initiator has a thin layer of insulating andspacing material, for example, paper, cardboard, or plastic, positionedbetween the match assembly and the sides of the shell member to preventphysical contact of the match assembly and the shell wall.

The present invention also contemplates a delay explosion initiatorwhich includes a match assembly in accord with the present invention.Generally a delay explosion initiator of the present invention includesa metallic shell, an explosive charge positioned in one end, a primercharge positioned in firing relation to the base charge and a delayelement which includes a delay train positioned in firing relation tothe primer charge. A match assembly in accord with the present inventionis positioned in firing relation to the delay train.

Now referring to the drawings wherein similar numerals denote similarcomponents throughout the several views: FIGURE 1 is a front elevationof an initiator match in accord with the present invention; FIGURE 2 isa side view partly in section of the match shown in FIGURE 1; FIGURE 3is a sectional elevation of an electrical explosion initiator containinga match of the present invention, and; FIGURE 4 is a sectional elevationof a delay electrical explosion initiator containing a match of thepresent invention.

Looking now in detail at the drawings, and in particular, at the matchshown in FIGURES 1 and 2. Metallic match tabs 11 and 13, suitably of atrapezoidal shape, have a narrowed bottom portion 15. Leg wires 17 and19 are attached to tabsll and 13 suitably by a soldered joint such as21. A layer of nonconducting material 12 electrically separates thetabs. A bridge wire 23 elecagape-A47 contact therewith is amatchcomposition 25 forming a match head 27. Suitably the match compositionis molded around the bridge wire. The match composition may be appliedto the match assembly by suspending the match composition in a lacquer,such as nitrocellulose,

which acts as a binder and leaves a flammable residue on drying, anddipping the bridge wire end of the match assembly in the suspension.Upon removing the match assembly from the suspension a layer of thesuspension clings to and covers the bridge wire. On drying a match headis formed. After the first layer, subsequent layers maybe applied.Suitable materials for the match ignition composition include, forexample, cuprous acetylide, diazodinitrophenol, leadmononitrorescorcinate, mixtures of lead mononitroresorcinate andpotassium chlorate, and

silver or lead azides.

A plug of semi-conductive material 29 extends through tabs 11* and 13and non-conducting layer 12-. Suitably plug 29 extends slightly beyondthe confines of the match tabs in' order to insure good electricalcontact with tabs 11 and 13 and leg wires 17 and 19. Plug 29 is suitablycomprised of a finely-divided metal, for example, aluminum, or acombination of aluminum and a suitable metal oxide suspended in a matrixof a relatively high melting point wax, for example, Acrawax.

FIGURE 3 is a sectional elevation showing a match assembly of thepresent invention incorporated in an,

electric explosion initiator. Shell 30 suitably of a metal such ascopper, brass'or aluminum, contains a base charge 31 in one end thereof.Base charge 31 is suitably a detonable material for example,pentaerythritol tetranitrate or tetryl. A primer charge 33 is positionedadjacent and in detonating relation to the base charge 31. Primer charge33' is suitably comprised of mannitol hexanitrate or diazodinitrophenol.Adjacent and in detonating relation to the primer charge 33 is a matchassembly similar to that shown in FIGURE 1 and FIGURE 2. A papercylinder 35 is positioned between the inside wall of shell 30 and thematch assembly in order that physical contact between the shell wall andthe match assembly is prevented. Leg Wires 17 and 19 are connected withthe match assembly and extend out of' shell 30 through a sealing plug37" suitably'of nubberor plastic.

FIGURE 4 is a sectional elevation showing a match assembly of thepresent invention incorporated in a delay electric explosion initiator.The components of the initiator shown in FIGURE 4 correspond with thecomponents of the initiator shown in FIGURE 3 except that adjacent andin firing position to primer change 33 is a delay element 43 containinga delay powder train 45, for example, a mixture of a powdered mixture ofa zirconium-nickel alloy and red lead. The match assembly ispositionedin-firing relation to the delay powder train45.

In operation any ditference of high potential existing betweeri'the legwires 17 and 19 is equalized by a passage of potential through plug 29,rather than through bridge wire 23. The present invention also providesa discharge path for high potential existing on the leg wires-plugcircuit through the match tabs points, for example, 339 and 41, throughinsulation 35 to the inside of metallic shell 30. The high potentialpath made available elfectively circumvents the bridge wire andfacilitates the dissipation of the potential charge in a harmlessmanner, that is, from the outside shell wall to ground either directlyor by contact with a grounded object.

When exposed to elevated temperature conditions which prevail within aninitiator when electrical arcing occurs, the semi-conductiveplugpartially melts and provides a path of low resistance between theleg wires. The path available to the electrical current aborts violentarcing conditions within the initiator and thereby prevents malfunctionof the initiator.

Table I shows the results of .a series of comparative electrostatictests conducted using initiators containing.

semi-conductive plugs of the prior art and initiators'containing plugsinaccord with the present invention. The prior art detonators containeda plug of semi-conductive materials positioned within the confines ofthe detonator shell. The plug was positioned so that it surrounded andwas in intimate contact with bared portions of the leg wires andextending to close proximity with the inside shell wall. The plug isspaced from the shell wall by a distance substantially less than thedistance between-either of the leg wires and the shell wall in the locusof the ignition composition. Thus, a static charge may be conducted tothe edge of the semi-conductive plug-body and allowed to discharge tothe shell Wall. In this manner the static charge may be grounded to theshell outside the locus of the ignition composition. Testseries 1 showsthe results of a series of tests conducted on prior art initiators. Testseries 2 shows the results of similar tests on the initiators of thepresent invention. The tests were made to determine the sensitivity ofthe initiators to an electrostatic charge. Each initiator of'each serieswas separately tested by electrically connecting it to a condenserpreviously charged by a high potential power source. In carrying out thetest, the leg wires of the initiator were shunted and then electricallyconnected to a source of condenser discharge, the shell of the initiatorwas electrically connected to a ground source, and" incrementalincreasing amounts of condenser energy was applied to the shunted legwires until detonation occurred. The minimum condenser energy requiredtofire the initiator or, if the initiator failed to fire, the maximumcharge which could be' delivered-from the test equipment wasreoorded.For example, in test series 1 shown in Table I, 25 prior art initiatorseach containing a protective plug comprised of 60% by weight of powderedaluminum in a wax matrix were tested one at a time by connecting. theinitiator shell to ground, shunting the leg wires and connecting theshunted leg wires by means of a suitable switch to a condenserpreviously changed from an electrical source. In test series 1, theinitial test energy was 0.5 joule at 10 kv. which was discharged throughthe detonator to be tested. If the detonator did not fire, the energytest level, using 10 kv., was raised in increments of 0.5 joule testingthe detonator at each energy level. The maximum energy test level, using10 kv., was 5.0 joules (0.10 mfd.).

If the detonator had not detonated when this energy test level wasreached, the 0.10 mfd. condenser was charged denser when charged from a13 kv. source. The highest energy level required'to initiate any oneinitiator in the group was 8.4 joules. The lowest energy levelsuflicient to fire one in the group was 1.5 joules. The average amountofelectrical energy required to fire the series was 5.1 joules. Testseries '2 shows the results obtained when 50 initiators of the presentinvention containing protective plugs made up of by weight of .powderedaluminum in a wax matrix were tested in a similar manner to those intest series 1. It will be noted that 12 initiators of test series 2 didnot fire when exposed to an electrical energy level of 11.2 joules,which was the capacity of the static 11.2 joules, thus the actual energylevel required to fire the series Would be higher than the 7.7 joulesshown in Table I. Test series 3 was carried out in a similar manner andthe average energy level required to fire the invalue. In each test alead plate was placed beneath the initiator and examined after firing todetermine the chiciency of the initiator. The firings were judged fromgood to bad by designations of from A to F in the plate itiators wascalculated on the same basis as Test Series 2 tests. Test series 16 wasconducted in a similar manner TABLE I Energy (Joules) No. of Type ofPlug No. Tested no-fires at 11.2 High Low Average joules Test Series 1Leg Wires 60/40, aluminum-wax s 25 8. 4 1. 5 5. 1 Test Series 2 Matchhead 90/10, aluminum-wax 50 1. 7. 7+ 12 Test Series 3 Match head 95/5,aluminum-wax .s 50 1. 5 5. 8+ 8 In general initiators which exhibit 0%detonation at the energy level of 1 joule at 10 RV. are considered to beto test series 1315, and 1723, except that a 420 volt power line sourceof electrical energy was utilized.

TABLE III Type or Plug No. Tested Potential Amperage Results Test Series13 Leg wires 60/40 aluminum-wax. 50 240 10 4 plug blowouts.

Normal functioning all Test Series 14 Match head 95/5 aluminum-Wax. 252A0 10 A plates. Test Series 15 Match head 95/5 aluminum-wax. 50 240Nirmial functioning all p a s. Test Series 16 Match head 95/5aluminum-wax. 50 420 15 Norlnial firing all A p a es.

TABLE IV Test Series 17 18 19 20 21 22 23 Percent Aluminum 75 75 75 7575 75 75 Percent Metal Oxi 20 2O 20 20 20 20 20 Metal Oxide SnOz M1102CuO PbsOl FeaOl K2Or 01 BaCrOr Percent Acrawax O 5 5 5 5 5 5 5 Number ofInitiators Tested- 25 25 25 25 25 25 25 Potential (Volts A.C.) 230 230230 230 230 230 230 Amperage 10 10 10 10 10 l0 10 Results 1 Normalfiring, no blowouts, all A plates. free from the danger of accidentalfiring due to extrane- Having thus described the invention, what isclaimed ous electricity normally encountered during their use. is. TableII shows the results of a series of tests using 1. Amatch assemblycomprising initiators containing plugs in accordance with the presa pairof conductive tabs having a bottom portion, ent invention wherein theleg wires of each initiator were said tabs separated by a layer ofnon-conductive mashunted and electrically connected to a source of conterial, denser discharge and the shell of the initiator was eleca bridgewire connecting said tabs along said bottom trically connected to aground source. The results in portion, Table II were obtained byexposing the initiators to an an ignition composition in ignitableposition with said energy of 1.0 joule at 10 kv. bridge wire,

TABLE II SHUNT-TO-SHELL STATIC TESTS AT 1 JoULE-m KV. 0F ALUMINUM-METALOXIDE-AORAWAX o COMBINATIONS Test Series 4 5 6 7 8 9 10 11 12 PercentAluminum 95 75 75 50 75 75 75 70 70 Percent Metal Oxide 20 20 45 20 202O 25 25 Metal Oxide Pbafi S1109 FeaOl F0304 0110 M110: K Or O1 BaOrO;Percent Acrawax C 5 5 5 5 5 5 5 5 5 Number of Initiators Tested- 25 2525 25 25 25 25 25 25 Percent Firing 0 0 0 0 0 0 0 0 0 Number Failing toFire 25 25 25 25 25 25 25 25 25 Tables III and IV are compilations oftest results in said tabs havng a portion broader than said bottomregard to the arc-resistance. Test series 1423 are test portion, resultsof initiators of the present invention. In test said tabs and saidnon-conducting material having a series 13, shown in Table III, 50 priorart initiators were perforation therethrough, and evaluated. Table IV isa compilation of test results of a plug of semi-conductive materialpositioned in said the arc resistance of initiators containing a plug ofthe perforation in contact with each member of said pair presentinvention comprising a mixture of aluminumof tabs. metal oxide and wax.In each test series of Tables III 2. The match assembly of claim 1wherein and IV each initiator was individually tested by applying thesemi-conductive material is a mixture of a finely an electrical currentfrom a 60 cycle AC. power line to divided metal and an insulatingmaterial. the leg wires for a period of 5 seconds. In each test 3. Thematch assembly of claim lwherein series, a rheostat was connected inseries with the test the semi-conductive material comprises a mixture ofinitiator to initially adjust the current to the desired aluminum and aninsulating material containing between about 80 to about 99% by weightof aluminum.

4. The match assembly of claim 1 wherein the semi-conductive plugextends in an outward direction beyond the surface of said tabs.

5. The match assembly of claim 1 wherein the semi-conductive plug has across-sectional area between about 0.0028 and about 0.0078 square inch.

6. The match assembly of claim 1 wherein the semiconductive material isa mixture of a finely divided metal, a finely divided metal oxide and aninsulating material.

7. The match assembly of claim 1 wherein the semiconductive materialcomprises a mixture of aluminum, a metal oxide and an insulatingmaterial.

8. The match assembly of claim 7 wherein the metal oxide is selectedfrom the group consisting of Pb O SnO F6304, C110, M110 K2CI'207 andBaCrO 9. The match assembly of claim 1 wherein the semiconductivematerial comprises a mixture of from about 45% to about 98.5% ofaluminum, from about 0.5% to about 50% metal oxide and from about 1% toabout 5% wax.

10. An electric explosion initiator comprising a shell member containingan explosive charge positioned in said shell member,

a match head positioned in firing relation to said charge,

said match head comprising a pair of conductive tabs having a bottomportion,

said tabs separated by a layer of non-conductive material,

said tabs and layer of non-conductive material having a perforationtherethrough,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

said tabs and said non-conducting material in close physical contactwith a plug of semi-conductive material positioned in said perforationin contact with each member of said pair of tabs,

a pair of leg wires entering said shell member,

separate members of said pair of leg wires electrically connected toseparate members of said pair of tabs, and

a non-conductive shield positioned between said pair of tabs and saidshell wall.

11. The electric explosion initiator of claim wherein thesemi-conductive material is a mixture of a finely divided metal and aninsulating material.

12. The electric explosion initiator of claim 10 wherein thesemi-conductive material comprises a mixture of aluminum and aninsulating material containing between about 80 to about 99% by weightof aluminum.

13. An electric explosion initiator comprising a shell member containingan explosive charge positioned in one end of said shell member,

a match head positioned in firing relation to said charge,

said match head comprising a pair of conductive tabs having a bottomportion,

said tabs separated by a layer of non-conductive material,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

said tabs and said non-conducting material having a perforationtherethrough, and

a plug of semi-conductive materials positioned in said perforation incontact with each member of said pair of tabs,

a pair of leg wires entering said shell member,

separate members of said pair of leg wires electrically connected toseparate members of said pair of tabs, and

a non-conductive shield positioned between said pair of tabs and saidshell wall.

14. The initiator of claim 13 wherein the plug in said match extends inan outward directio beyond the surface of said tabs.

15. The initiator of claim 13 wherein the semi-conductive material is amixture of a finely divided metal and an insulating material.

16. An electric explosion initiator comprising a shell member containingan explosive charge positioned in said shell member,

a delay element positioned in firing relation to said charge,

a match head positioned in firing position to said delay element,

said match head comprising a pair of conductive tabs having a bottomportion,

said tabs separated by a layer of non-conductive material,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

said tabs and said non-conducting material having a perforationtherethrough, and

said tabs and said non-conducting material in close physical contactwith a plug of semi-conductive material positioned in said perforationin contact with each member of said pair of tabs,

a pair of leg wires entering said shell member,

separate members of said pair of leg wires electrically connected toseparate members of said pair of tabs, and

a non-conductive shield positioned between said pair of tabs and saidshell wall.

17. The electric explosion initiator of claim 16 wherein thesemi-conductive material is a mixture of a finely .divided metal and aninsulating material.

18. The electric explosion initiator of claim 16 wherein thesemi-conductive material comprises a mixture of aluminum and aninsulating material, said mixture containing between about and about 99%by weight of aluminum.

19. An electric explosion initiator comprising a shell member containingan explosive charge positioned in one end of said shell member,

a delay element positioned in firing relation to said charge,

a match head positioned in firing position to said delay element,

said match comprising a pair of conductive tabs having a bottom portion,

said tabs separated by a layer of non-conductive material,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

said tabs and said non-conducting material having a perforationtherethrough, and

1 l 1 2 a plug of semi-conductive material positioned in said thesemi-conductive material is a mixture of a finely perforation in contactwith each member of said pair divided metal and an insulating material.of tabs, a pair ofleg wires entering said shell member, References Citedby the Exammer separate members of said pair of leg Wires electrically 5UNITED STATES PATENTS connected to separate members of said pair oftabs, 1,868,224 7/1932 Schurmann 2,173,270 9/1939 Burrows 102-28 anon-conductive shield positioned between said pa1r 2,974,590 4/1961Ram;r 1O2 28 of tabs and Said shell wall- 3,041,972 7/1962 Ball 102-2s20. The initiator of claim 19 where-in 10 3 194 160 7/1965 Spillane eta1 102-28 the plug in said match extends in an outward direction beyondthe Surface of Said tabs SAMUEL FEINBERG, Przmary Examiner.

21. The initiator of claim 19 wherein V. R. PENDEGRASS, AssistantExaminer.

1. A MATCH ASSEMBLY COMPRISING A PAIR OF CONDUCTIVE TABS HAVING A BOTTOMPORTION, SAID TABS SEPARATED BY A LAYER OF NON-CONDUCTIVE MATERIAL, ABRIDGE WIRE CONNECTING SAID TABS ALONG SAID BOTTOM PORTION, AN IGNITIONCOMPOSITION IN IGNITABLE POSITION WITH SAID BRIDGE WIRE, SAID TABSHAVING A PORTION BROADER THAN SAID BOTTOM PORTION, SAID TABS AND SAIDNON-CONDUCTING MATERIAL HAVING A PERFORATION THERETHROUGH, AND A PLUG OFSEMI-CONDUCTIVE MATERIAL POSITIONED IN SAID PERFORATION IN CONTACT WITHEACH MEMBER OF SAID PAIR OF TABS.